1. Field of the Invention
The invention relates to a rolling bearing.
2. Description of the Related Art
Many rolling bearings are used for various types of industrial equipment. A rolling beating includes an inner ring, an outer ring, a plurality of rolling elements, and a cage. The rolling elements are interposed between the inner ring and the outer ring. The cage holds the rolling elements.
For the rolling bearing, rotational resistance is preferably reduced. For example, a rolling bearing described in Japanese Patent Application Publication No. 2009-281585 (JP 2009-281585 A) is configured to restrain a lubricant in a bearing exterior from entering a bearing interior. That is, the rotational resistance includes a component (stirring resistance) resulting from stirring, by the cage, of a lubricant present in the bearing interior. To reduce the stirring resistance, the lubricant in the bearing exterior is preferably made less likely to enter the bearing interior. Thus, as depicted in FIG. 5, clearances A1, A2 between a cage 93 and each of an inner ring 91 and an outer ring 92 are reduced in size. In this rolling bearing, the cage 93 is a snap cage having an annular portion 94 located on a first side in an axial direction and a plurality of cage bars 95. The cage bars 95 extend from the annular portion 94 toward a second side in the axial direction. The clearance A1 between the annular portion 94 and a shoulder portion 97 of the outer ring 92 is reduced in size, and the clearance A2 between the annular portion 94 and a shoulder portion 99 of the inner ring 91 is also reduced in size.
In the rolling bearing described in JP 2009-281585 A, an axially-first-side (bearing-exterior-side) side surface 90 of an annular portion 94 of the cage 93 is an inclined surface that is inclined toward the first side in the axial direction as the inclined surface extends toward the outer ring 92 as depicted in FIG. 5. In this case, rotation of the bearing causes the lubricant in the bearing exterior to flow from the inner ring 91 toward the outer ring 92 due to a centrifugal force resulting from the rotation. On the first side in the axial direction with respect to the cage 93, the lubricant flows along the inclined side surface 90 as depicted by arrow F in FIG. 5. The lubricant having flowed along the side surface 90 has a component traveling toward the first side in the axial direction. Thus, the lubricant is less likely to enter the bearing interior through a clearance A1 between the annular portion 94 and the outer ring 92. This enables a reduction in the stirring resistance in the rolling bearing and thus in the rotational resistance to the rolling bearing.
In the rolling bearing depicted in FIG. 5, the lubricant having flowed along the inclined side surface 90 impinges on an inner peripheral surface of the shoulder portion 97 of the outer ring 92 and turns in another direction. Then, most of the lubricant flows toward the first side in the axial direction, with a portion of the lubricant traveling toward the second side in the axial direction. The lubricant flowing toward the second side in the axial direction flows directly between the annular portion 94 and the shoulder portion 97 of the outer ring 92 and enters the bearing interior, causing stirring resistance.
The lubricant may contain relatively hard foreign matter, for example, abrasion powder. In this case, when the lubricant in the bearing exterior is likely to enter the bearing interior, the foreign matter contained in the lubricant may be trapped, for example, between the outer ring and the rolling elements or between the inner ring and the rolling elements. The foreign matter may damage a raceway surface and the like, and peel-off or the like may start at the damaged point, shortening the life of the bearing. As described above, the lubricant in the bearing exterior is preferably made less likely to enter the bearing interior.